Powder paints do not contain organic solvents, and the corresponding lack of toxicity coupled with contemporary environmental concerns, such as air pollution and the like, has caused annual increases to occur in the consumption of the resin compositions used for powder paints (hereinafter referred to as powder-paint resin compositions). Widely used as powder-paint resin compositions are, for example, compositions whose main component is reactive functional group-containing curable organic resin, e.g., acrylic resin, polyester resin, epoxy resin, and the like, and which may contain any of various curing agents on an optional basis. However, the cured coatings afforded by the cure of such compositions suffer from an inadequate weathering resistance. This has led to various investigations into powder-paint resin compositions that would have the capacity to produce highly weathering-resistant cured coatings. For example, Japanese Patent Application said Open [Kokai or Unexamined] Number Sho 52-66536 [66,536/1977] proposes a powder-paint resin composition comprising hydroxyl-functional polyester resin with an acid number no greater than 40 and straight-chain organopolysiloxane bearing silicon-bonded methoxy. Japanese Patent Application Laid Open [Kokai or Unexamined] Number Sho 58-168667 [168,667/1983] proposes a powder-paint resin composition comprising thermosetting organic resin and epoxy-functional alkoxysilane. Japanese Patent Application Laid Open [Kokai or Unexamined] Number Sho 59-59751 [59,751/1984] proposes a powder-paint resin composition comprising thermosetting organic resin and straight-chain organopolysiloxane having a viscosity of 10 to 10,000 centistokes and functionalized with the amino, mercapto, carboxyl, or phosphate group.
However, each of these powder-paint resin compositions suffers from an unsatisfactory curability and unsatisfactory electrostatic properties (wraparound). Moreover, the coatings afforded by the cure of these compositions still evidence an inadequate weathering resistance. Another problem with these coatings is their unsatisfactory mechanical properties.
The present inventors achieved the present invention as the result of extensive investigations directed to solving the problems described above.
In specific terms, then, the object of the present invention is to provide a powder-paint resin composition that exhibits an excellent curability and excellent electrostatic properties (wraparound) and that generates a cured coating with an excellent appearance, excellent resistance to weathering, and excellent mechanical properties.